Family-based treatment (FBT) produces correlated weight changes within child-parent dyads in the short- and long-term. The present study aimed to further elucidate these correlated weight changes by modeling the intra-family effect of weight during FBT and maintenance treatment while controlling for correlations within time-points and the effects of the individual on their own weight change.
172 child-parent dyads with overweight/obesity (child mean BMI z-score (BMIz)=2.16±0.39; parent mean BMI=37.9±9.4 kg/m^2) completed 4 months of FBT and were randomized to one of three 8-month maintenance treatments (Social Facilitation Maintenance [SFM] High dose, SFM Low dose, or Control). Weight/height were measured at 0-, 4-, and 12-months. Multiple wave autoregressive models with cross-lagged paths simultaneously estimated the participant’s effect on their own (actor effect) and the other dyad member’s (partner effect) weight across time using the actor-partner interdependence model.
Overall model fit was good (RMSEA=.08; CFI=.99). Actor paths were significant over time such that child BMIz predicted BMIz at each following time point, and similarly for parent BMI predicting subsequent BMI (p’s<.001). Partner paths were significant for child BMIz predicting parent BMI at 4-months (p<.05). A post-hoc test of maintenance condition as a moderator of shared weight change models during maintenance was significant (p<.05), such that child BMIz predicted parent BMI from 4- to 12-months in dyads in SFM High and SFM Low, but not Control. Parent BMI did not predict child BMIz at any time point.
These findings point to the important role of intra-family influence on child and parent weight loss, suggesting that parents may benefit from child weight loss when in FBT and SFM treatment. Future research should elucidate mechanisms explaining these relationships to optimize child/parent success in clinical interventions for weight loss maintenance.